Radar transducers of this general type are widely used for many purposes but one particular end use is that on vehicles for detecting vehicle speed. The transducer forms part of the vehicle control system and thus communicates with the vehicle control system by providing suitable output signals at a number of leads of an output cable. The output signals are not standardized so that different end uses or vehicles often require different output signals to be provided by the transducer. Such transducers are often relatively complicated in manufacture due to the requirement for metallic shielding to avoid interference of the output signals from extraneous electro magnetic radiations.